The invention relates to a mass spectrometer arrangement.
Mass spectrometric measuring methods are currently applied in manifold type and manner in the field of process engineering, technology and product development, medicine and in scientific research. Typical application areas are herein leakage testing of structural parts in various industrial fields, quantitative determination of the composition and purity of process gases (partial pressure determination of gas fractions), complex analyses of reactions on surfaces, investigation and process monitoring in chemical and biochemical procedures and processes, analyses in the area of vacuum engineering, for example of plasma processes, such as, for example, in the semiconductor industry, etc.
For this purpose a multiplicity of different methods for the physical mass separation of particles has been developed and, correspondingly, measuring instruments for practical use have been realized. All of these measuring instruments have in common that they require vacuum for their operation. The neutral particles to be analyzed are inducted into the vacuum of the system and ionized in a reaction zone. This component is conventionally referred to as ion source. The ionized particles are subsequently conducted out of this zone with the aid of an ion optics and supplied to a system for mass separation. There are various concepts for the mass separation. For example, in one case the ions are deflected via a magnetic field, wherein, depending on their mass, the particles are subject to large deflection radii which can be detected. Such a system is known by the name sector field mass spectrometer. In a further, very widely used system the mass filter is comprised of an electrostatic system of four rods into which the ions are shot. On the rod system is impressed a high-frequency alternating electrical field, whereby the ions execute oscillations of different amplitude and trajectory, which can be detected and separated. Among experts this system is known as a quadrupole mass spectrometer. This mass spectrometer has various advantages such as, in particular, high sensitivity, wide measuring range, high measurement repetition rate, small dimensions, arbitrary mounting orientation, direct compatibility in important applications in vacuum engineering and good operability.
The ion sources of these known mass spectrometers conventionally employ a thermionic cathode which includes a heated filament, thus an incandescent cathode, for the generation of electrons which ionize the neutral particles under bombardment. While on this conceptual basis, the quality, for example of the quadruple spectrometer, is already quite good, the thermionic cathodes utilized, however, have various disadvantages which then also have an overall negative effect on the mass spectrometer.
One problem is that from an incandescent cathode, material of the filaments is also always vaporized and thereby undesirable particles are superimposed on the particles to be measured, which increases the so-called signal noise and consequently negatively effects the measuring accuracy or falsifies the measurement signal.
A further problem consists in that on or in the proximity of the hot filament chemical reactions take place with the particles to be measured and thereby the measurement is falsified and the resolution decreased. The emission of light, thus of photons which can interact, is herein of disadvantage. The hot arrangement leads additionally to increased temperature fluctuations which result in increased drift behavior and poor reproducibility of the measurement results. A filament, moreover, is vibration-sensitive, which can lead to undesirable signal fluctuations (microphony) or even to breakage under severe shock.